1. Field of the Invention
The present invention relates to the transfer of data, such as Fibre Channel, GbE (Gigabit Ethernet), Ethernet or ESCON (Enterprise System Connection) data, across SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy) transport networks, and more particularly to the transfer of data across such transport networks without unnecessarily signaling or propagating alarms for temporary faults.
2. Discussion of the Relevant Art
Modern communication networks are comprised of data networks and transport networks that transmit data formatted according to different protocols or standards. For example, data networks may transmit data using the Fibre Channel, GbE, Ethernet or ESCON standards. Optical transport networks may typically use either the SONET or SDH standards.
The SONET standard is an American National Standards Institute standard for synchronous data transmission on optical media. The international equivalent of the SONET standard is the synchronous digital hierarchy (SDH) standard, developed by the International Telecommunications Union (ITU). These two standards ensure that digital networks can interconnect internationally and that existing conventional transmission systems can take advantage of optical media through tributary attachments. SONET provides standards for a number of line rates up to the maximum line rate of 9.953 gigabits per second (Gps). Actual line rates approaching 20 gigabits per second are possible. SONET is considered to be the foundation for the physical layer of the broadband ISDN (Integrated Services Digital Network). SONET/SDH networks transport data to data networks such as Ethernet, GbE, Fibre Channel, Escon etc.
Ethernet is probably the most popular local area network technology. Ethernet, which is included in the IEEE 802.3, standard was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network). Other corporations including DEC and Intel have contributed to the development of Ethernet. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet may also be used in wireless LANs. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol. Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards.
Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second), and 10-Gigabit Ethernet provides up to 10 billion bits per second. Gigabit Ethernet is based on the same Ethernet frame format and protocol used in local area networks (LANs). Gigabit Ethernet is also defined in the IEEE 802.3 standard, and it is often used as the backbone in many enterprise networks. Gigabit Ethernet is carried primarily on optical fiber (with very short distances possible on copper media). Existing Ethernet LANs with 10 and 100 Mbps cards can feed into a Gigabit Ethernet backbone. A newer standard, 10-Gigabit Ethernet, is becoming available.
Fibre Channel is a technology for transmitting data between computer devices at data rates of up to 1 or 2 Gps and possibly even 10 Gbps in the future. Fibre Channel is well suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives. Since Fibre Channel is three times as fast, it has begun to replace the Small Computer System Interface (SCSI) as the transmission interface between servers and clustered storage devices. Fibre channel is more flexible, and devices can be as far as ten kilometers (about six miles) apart if optical fiber is used as the physical medium. Optical fiber is not required for shorter distances, however, because Fibre Channel also works using coaxial cable and ordinary telephone twisted pair.
ESCON (Enterprise Systems Connection) is a marketing name for a set of IBM and vendor products that interconnect S/390 computers with each other and with attached storage, locally attached workstations, and other devices using optical fiber technology and dynamically modifiable switches called ESCON directors. In IBM mainframes, the local interconnection of hardware units is known as channel connection (and sometimes as local connection to distinguish it from remote or telecommunication connection). ESCON's fiber optic cabling can extend this local-to-the-mainframe network up to 60 kilometers (37.3 miles) with chained directors. The data rate on the link itself is up to 200 Mbps (million bits per second) and somewhat less when adapted to the channel interface. Vendor enhancements may provide additional distance and higher amounts of throughput to an ESCON network.
Referring now to FIG. 1, a first data network 11 and second data network 12 are illustrated as being coupled together via an optical transport network 13, such as a SONET or SDH network. The first data network 11, which could include a Fibre Channel, Ethernet, GbE or ESCON data network is coupled to the SONET/SDH transport network 13 via a router/SAN device 14 and a data to transport network conversion device 15. A SAN (storage area network) data gateway router is a hardware solution that enables the attachment of SCSI storage systems to Fibre Channel adapters on specific Intel-based servers running Windows NT and UNIX-based servers from IBM and Sun Microsystems. An example of such a device is the IBM SAN Data Gateway Router 2108-R03. Likewise, the second data network 12, which could also include a Fibre Channel, Ethernet, GbE or ESCON data network is coupled to the optical transport network 13 via a router/SAN device 16 and a data to transport network conversion device 17.
In a conventional network, a fault can occur at an output 1 of the data to transport network conversion device 15. The fault could include a fiber break, a loss of frame (LOF), a loss of signal (LOS), etc. The fault would be detected at the SONET/SDH transport network port 2 of the data to transport network conversion device 17. A signal would then be propagated from the port 3 of the data to transport network conversion device 17. The signal could indicate a fault, such as laser shutoff, NOS (network operating system) problem, OLS (optical label switching) problem, etc. The router/SAN (System Area Network) device 16 would then signal a link down condition to the second data network 12.
If such a scenario occurs, the transport of Fibre Channel, Escon, Ethernet or GbE data across the SONET/SDH network 13 requires translation of SONET/SDH network defects/alarms into Fiber Channel and Ethernet defects/alarms. This translation allows the router/SAN device 16 and/or the Fiber Channel and Ethernet network 12 to process the SONET/SDH defect/alarm as if it occurred in the data realm. When the SONET/SDH network 13 is totally unprotected, this translation may occur instantaneously. However, if the SONET/SDH network 13 is protected, for example, using a BLSR SONET protection scheme, the error may not be corrected fast enough before the defect/alarm translation occurs. During this switching time, if the temporary error is translated to the data network 12, a link down condition may be signaled and propagated throughout the data network 12, negating the fast restoration of the SONET/SDH network 13. Accordingly, there is a need to prevent relatively brief and correctable faults in the SONET/SDH network 13 from being signaled and propagated throughout the data network 12. One solution might include a built-in delay for each router/SAN device connected to the SONET/SDH transport network. However this delay would be used in all cases, including SONET/SDH unprotected and protected scenarios.
Several vendors sell products that allow the transport of Ethernet data over a SONET/SDH line. One such product is the Riverstone RS 38000 router, but these systems do not provide a flexible delay of fault propagation to allow for proper interoperation of the data and transport networks. In such schemes, a hold-off timer in a router/SAN device may be used when there are overlapping protection schemes. This generically will cause, for example, a router/SAN device to hold-off its fault acknowledgement and processing logic when detecting any fault. This will allow an optical network's protection switch to complete, but it is not a satisfactory solution.
Accordingly, there is a need for a technique that introduces a dynamic delay in the SONET/SDH network allowing it to only be applied in the SONET/SDH protected network scenario and centralizing the configuration of the delay for all connected data networks.